1. Field of the Invention
This invention relates to a process for separating a fraction substantially comprising asphaltenes from heavy hydrocarbon materials and then treating the separated fraction to crack and vis-break the same to produce additional liquid products having a reduced metals content.
2. Brief Description of the Prior Art
Many methods of extracting various fractions from bituminous materials have been disclosed previously in the prior art. Perhaps the most well known of these is termed "propane extraction" in which asphaltic materials are separated from heavy hydrocarbons to produce deasphalted oils and an asphaltene-containing residue by means of a single solvent extraction step using propane as the extractant.
In that it is desirable to obtain the greatest possible quantity of oils from a heavy hydrocarbon material such as a reduced crude, other extraction techniques have been developed. U.S. Pat. No. 2,940,920, assigned to the same assignee as is the present invention, discloses a process capable of effecting a deeper cut in heavy hydrocarbon materials than is available by means of propane extraction. That patent discloses effecting the separation by using high temperature-pressure techniques and by using pentane as one of a group of suitable solvents. Such practice permits a deeper cut to be made in the heavy hydrocarbon material and produces an asphaltene-containing residue having a higher viscosity than that produced by propane extraction.
Normally, the asphaltene-containing residue also will contain a substantial portion of any organometallic compounds which are present in the heavy hydrocarbon material. This residue, because of its high viscosity and metals content, has limited commercial utility. The residue can be used as a soil conditioner, asphalt hardener, printing ink pigment, paper sizing agent and solid granular insulator. The physical and chemical properties of the residue substantially limit its use as a liquid fuel even when diluted with hydrocarbon cutter stocks.
It would be desirable to convert the asphaltene-containing residue into lighter products by vis-breaking or thermal pyrolysis under controlled conditions to acceptable lower viscosity products suitable for use as liquid fuels. Various processes for vis-breaking heavy hydrocarbon materials by thermal pyrolysis are disclosed in U.S. Pat. Nos. 2,695,264; 2,900,327; 3,234,118 and 3,349,024.
Prior attempts to produce liquid products from asphaltenes have had limited success. When an attempt has been made to vis-break or thermally pyrolyze the asphaltenes, coking has occurred in the process equipment. Coking occurs when a feed is not maintained in a turbulent flow condition within the process equipment at the high temperatures at which the equipment operates. The high viscosity of the asphaltenes impedes maintaining the same in the turbulent flow condition necessary to prevent coking. This results in a low yield of desired vis-broken product and a short on-stream time before coking of the feed causes a termination of process operation. The coke then must be removed from the equipment manually or by burnout with injected air.